Co-pending and co-assigned U.S. patent application Ser. No. 09/539,707 filed on Mar. 31, 2000, and entitled METHOD AND SYSTEM FOR ESTABLISHING CONTENT-FLEXIBLE CONNECTIONS IN A COMMUNICATIONS NETWORK teaches a technique for establishing an open connection (OP-N), mapped across a communications network. The OP-N connection is “concatenatable”, in that an end user can transport arbitrarily concatenated signal traffic through the OP-N connection. In principle, virtually any combination of concatenated and non-concatenated signals may be used, up to the bandwidth capacity of the OP-N connection. The traffic mixture (i.e., the mix of concatenated and non-concatenated traffic) conveyed through the OP-N connection can be selected by the end user to satisfy their requirements, and may be changed by the end user as those requirements change, without requiring re-configuration of the OP-N connection. For example, with an OP-60 connection (i.e. N=60, so that the connection has a bandwidth capacity equivalent to an Optical Carrier OC-60 signal) an end user could arbitrarily change from a traffic mix of five STS-12c signals to one OC-48c and 12 (unconcatenated) STS-1 signals or two STS-24 and two STM-4 signals as required. Other traffic combinations are also possible, all at the discretion of the end user, and without intervention from a network service provider.
A limitation of the OP-N connection is that, although it can incorporated multiple channels, in general, the bandwidth of the highest capacity channel (e.g. a wavelength in a Wave Division Multiplexed—WDM, or Dense Wave Division Multiplexed—DWDM network) limits connection size. Thus, if the highest capacity channel of the OP-60 connection operates at a bit-rate of 2.488 GHz, then an OC-48c is the largest connection that can be supported by the OC-60.
However, it may be desirable to transport high bandwidth signals that exceed the capacity of any one channel of an OP-N connection. For example, it may be desirable to transport an OP-192 signal (which would require a line rate of 9.953 GHz to be carried on a single channel), or higher, using an OP-N connection in which the maximum line rate of any one channel is only 2.488 GHz.
Inverse multiplexing, in which a higher rate signal is distributed across several lower rate signals and then recombined at an end node, is known in the art. For example, U.S. Pat. No. 6,002,692 (Wills) teaches a system in which a higher rate Synchronous Optical Network (SONET) signal (e.g. an OC-48c at a 2.488 GHz line rate) is inverse multiplexed into multiple Asynchronous Transfer Mode (ATM) cells that are then transported across a switch fabric through respective ports at a lower rate (e.g. 622 MHz). In cases where data of a single SONET frame is carried within two or more ATM cells, each of the cells is provided with a respective sequence number so that the cells can be placed into the correct sequence for reassembly of the original SONET frame.
The system of Wills is typical of packet-based inverse-multiplexing methods, in that it requires a significant amount of processing to separate the SONET frame into ATM cell payload; formulate ATM cell headers with assigned sequencing numbers; and then re-sequence the ATM cells prior to reassembly of the SONET frame. Such systems are not easily implemented at multiple gigabits per second line rates. Furthermore, such packet-based methods are not relevant to concatenation of SONET signals, where the lower-rate signals are SONET signals.
U.S. Pat. No. 5,710,650 (Dugan) teaches a system in which a high data rate OC-192 signal (at a 9.953 GHz line rate) is inverse multiplexed into four lower rate OC-48 signals (at a 2.488 GHz line rate) which are transported through respective parallel channels (wavelengths). The lower line rate within each channel provides increased dispersion tolerance, so that longer fiber spans can be used without regeneration of the signals. Misalignment between the OC-48 signals (due to the differing propagation speeds of the four wavelengths) is resolved by processing each of the OC-48 signals in parallel to extract their respective 48 STS-1 signals (each having a 51.840 MHz line rate). These STS-1 signals are then individually buffered and processed in parallel to eliminate any misalignment. Treating the signals in this way dramatically reduces the amount of misalignment which needs to be eliminated (in terms of the number of bits) and so reduces the required length of each realignment buffer. However, the parallel circuits required for independently processing each of the STS-1 signals at the low 51.840 MHz line rate greatly increases the cost of the processing circuitry, and imposes severe restrictions on the available concatenation schemes.
A further limitation of the above-noted prior art systems is that, in order to maintain arbitrary concatenatability within a multi-channel connection, it is necessary to maintain precise alignment of the payload data being transported by the data streams within their respective channels, so that the high-bandwidth signal can be reassembled at an end node. None of the prior art systems provides an efficient and reliable means of maintaining this precise alignment with an arbitrary traffic mixture.
Co-pending and co-assigned U.S. patent Application Ser. No. 09/522,593, filed Apr. 19, 2000, and entitled HYPER-CONCATENATION ACROSS MULTIPLE PARALLEL CHANNELS, teaches a method for aligning two or more data streams being conveyed within respective parallel channels. In this system, data signals (which may comprise an arbitrary mixture of concatenated and non-concatenated signal traffic) are inverse-multiplexed and transported hop-by-hop through a hyper-concatenated connection distributed across multiple parallel hyper-concatenated channels. At a downstream end of each hop (including at the end node), the hyper-concatenated data streams are aligned by a signal processor having a plurality of parallel interconnected channel processors. At the end node of the hyper-concatenated connection, the original data signals are recovered from the hyper-concatenated data streams.
In this context, the terms “hyper-concatenation” (used as a noun) and “hyper-concatenated connection”, refer to a multi-channel communications path that supports an arbitrary mixture of concatenated and unconcatenated signal traffic and a maximum connection size equal to the total bandwidth capacity of all of its member channels. When used as a verb, the term “hyper-concatenation” refers to either: a process of setting-up a hyper-concatenation (that is, designating member channels of the hyper-concatenated connection, and roles of each member channel); or to a process of inverse-multiplexing data signals for transport through the hyper-concatenated connection.
The term “hyper-concatenated channel” refers to a member channel of a hyper-concatenated connection. These channels are associated such that: a maximum difference in propagation delays of payload data through each of the channels is within a predetermined tolerance; and, at least at opposite ends of the hyper-concatenation, the channels are physically adjacent, and channel ordering is identical. Similarly, the term “hyper-concatenated data stream” refers to a data stream within a hyper-concatenated channel. It will be appreciated that the hyper-concatenated data streams within any one hyper-concatenated connection are sourced from a common point (a “start” node) in a communications network, and thus have substantially equivalent data and frame rates. However, hyper-concatenated data streams may well have differing propagation delays and independent timing jitter.
“Parallel channels” are channels of the communications network in which channel ordering is identical (at least at each end of a connection), and within which respective data streams are not subject to independent pointer processing.
Thus in the above-referenced co-pending application, bit-wise alignment between hyper-concatenated data streams in respective parallel hyper-concatenated channels is re-established at the downstream end of each hop. Bit-wise alignment of payload data within each data stream is maintained by conventional parallel pointer-processing (e.g. by passing stuff indications etc. between pointer processor state machines for adjacent channels) within each node participating in the hyper-concatenated connection.
A limitation of this method is that each node in the hyper-concatenated connection must be equipped with a signal processor for aligning the hyper-concatenated data streams. As a result, legacy Add/Drop multiplexers and cross-connects cannot participate in an end-to-end OP-N connection that includes a hyper-concatenation. In addition, the hyper-concatenated connections cannot be larger than the capacity of any node in the path because the connection cannot be split into parallel data streams processed by independent pointer processor state machines. This restriction limits the ability to deploy OP-N connection related services in the current optical network space.
Accordingly, a method for transporting arbitrarily concatenated signal traffic through a hyper-concatenated connection across independent pointer processors is highly desirable.